Interface Behavior and Impact Properties of Dissimilar Al/Steel Keyhole-Free FSSW Joints

Abstract

This work systematically investigates the interface behavior and impact properties of the keyhole-free friction stir spot welding (FSSW) of a dissimilar metal AA6082-T4 Al alloy and DP600 galvanized steel. The keyhole is eliminated by pin retraction technology. The welding process is in accordance with the welding temperature curve and the maximum temperature of the periphery of the shoulder, measured at about 500 °C. The transition layers were formed at the interface, in which the Al, Fe, and Zn elements form an inhomogeneous diffusion. A cloud cluster-like mechanical mixing of the Al and steel components is formed in the stirring zone. The impact toughness of the specimen with a welding parameter of 1000 rpm is the best. To a certain extent, the factors affecting the impact energy are not the maximum impact load but the maximum impact deformation. The maximum impact deformation directly reflects the post-crack propagation energy, which significantly affects its impact toughness. In addition, the impact fracture showed a mixed ductile and brittle fracture mode with a brittle–ductile transition zone. Most of the impact energy was absorbed by the ductile fracture.

Effect of Loading Methods on the Fatigue Properties of Dissimilar Al/Steel Keyhole-Free FSSW Joints

“…Figure 1 shows the schematic diagram and flow chart of the dissimilar Al/steel keyhole-free FSSW process [ 5 ]. The welding parameters are listed in Table 2 [ 5 ].…”

“…Figure 1 shows the schematic diagram and flow chart of the dissimilar Al/steel keyhole-free FSSW process [ 5 ]. The welding parameters are listed in Table 2 [ 5 ]. In the process of dissimilar Al/steel keyhole-free FSSW in Figure 1 a, the welding tool first rotates and plunges at speeds of ω and v p , respectively (as shown in Figure 1 a).…”

“…If the temperature is too high, too many IMCs will be formed. The joint at 1000 rpm has good plasticity, toughness and crack propagation resistance [ 5 ].…”

“…Compared with the traditional welding method, this technology has the advantages of high joint quality, small welding deformation, low residual stress, a green welding process and no pollution. It is widely used in the aerospace, shipping, and transportation industries and other fields [ 3 , 4 , 5 , 6 ].…”

“…To improve the mechanical properties of FSSW joints, Yoon et al adopted swept FSSW AL to expand the connect area and transfer the keyhole position, which improved the strength of the joint to a certain extent [ 3 ]. Zhang [ 5 ] and Dong [ 6 ] et al welded Al and steel by using retracted FSSW and refilled FSSW, respectively, which successfully eliminated the keyhole defects of the joints, which not only improved the appearance but also enhanced the mechanical properties of the joint. The keyhole-free FSSW is expected to replace riveting to achieve the same strength of connection performance, which can be widely used in the connection of the aircraft envelope.…”